It's a terrible feeling to have so much saliva that you feel like drowning during the radiation. The "bite block" sounds like the problem and it can not hurt to require a justification for using it. I never had any type of bite block, or stick etc for any of my three different rounds of radiation over 5 years.
I did try use my fluoride trays during the first round but they did generate too much saliva.
If the doctors are insistent on drowning your husband, then ask for a prescription for Robinul, which will stop the saliva.
I need to take it now for my MRI and Petscans since after the surgery and not being able to swallow, I have tremendous amounts of saliva and phelgm that I need to spit out constantly. The Robinul drys it up in a day or two.

Ativan is useful for the one hour procedure of Cyberknife so I could hold still that long, but not for IMRT unless there are anxiety issues.
Again, ask about the bite block, sometimes radiologists just do things because they always have done them without reqard for the individual patient. Put the burden on the doctor to solve the saliva problem that he is causing
Charm